TW201732518A - Capacitive fingerprint sensing device and method for capturing a fingerprint using the sensing device - Google Patents

Abstract

The present invention relates to a capacitive fingerprint sensing device for sensing a fingerprint pattern. The sensing device comprises a protective dielectric top layer having an outer surface forming a sensing surface to be touched by the finger; a two-dimensional array of electrically conductive sensing structures arranged underneath the top layer; readout circuitry coupled to each of the electrically conductive sensing structures to receive a sensing signal indicative of a distance between the finger and the sensing structure; and an electroacoustic transducer arranged underneath the top layer and configured to generate an acoustic wave, and to transmit the acoustic wave through the protective dielectric top layer towards the sensing surface to induce an ultrasonic vibration potential in a ridge of finger placed in contact with the sensing surface.

Description

Capacitive fingerprint sensing device and method for acquiring fingerprint using the same

The present invention relates to a fingerprint sensing device. In particular, the present invention relates to a capacitive fingerprint sensing device that includes an electroacoustic transducer and a method for acquiring a fingerprint using the sensing device.

Various types of biometric systems have been increasingly used in order to provide increased security and/or enhanced user convenience.

In particular, fingerprint sensing systems have been used in consumer electronics devices due to their small size, high performance, and user-recognized relationships.

Capacitive sensing is most commonly used in a wide variety of available fingerprint sensing principles (such as capacitive, optical, thermal, etc.), especially in this application, where size and power consumption are Important topic.

All capacitive fingerprint sensors provide a measurement that can represent each of a finger and a plurality of sensing structures slid across or placed on the surface of the fingerprint sensor The value of the capacitance between.

Since a capacitive sensor detects a finger based on a capacitance value between a finger and a sensor, the distance between the sensing surface and the sensing structure directly affects the acquired in the measurement. Contrast and resolution of fingerprint images. This has not been a problem in the past because the thickness of the cover material can be chosen to have a small pressure. However, according to new design trends, it is desirable to place the sensor under a thick glass cover and ultimately integrate the fingerprint sensor into a display configuration.

This presents a challenging issue. The root cause of this problem is not only related to the weakening of the capacitance signal due to the increase in the distance from the finger to the sensor. Commercially available capacitive touch sensors work well through thick glass covers. However, the problem is the loss of resolution and image contrast as the distance from the finger to the sensor increases. This is due to the fact that when the distance between the finger and the sensor is large, it is extremely difficult to distinguish the small capacitance change caused by the fingerprint path from the large background "average value", where the large background "average" It is the sum of all the ridges and valleys that are "visible" to the pixel.

Accordingly, it would be desirable to be able to provide a fingerprint sensor that overcomes some of the aforementioned difficulties associated with capacitive sensing with a thick outer cover layer.

In view of the above and other shortcomings of the prior art, it is an object of the present invention to provide an improved fingerprint sensing device for capacitive fingerprinting.

According to a first aspect of the present invention, there is provided a capacitive fingerprint sensing device for sensing a fingerprint pattern of a finger, the capacitive fingerprint sensing device comprising: a protective dielectric top layer having An outer surface to form a sensing surface that is touched by a finger; a two-dimensional array a conductive sensing structure of the column, disposed below the top layer; a read circuit system coupled to each of the conductive sensing structures to receive a sensing signal, the sensing signal indicating the finger a distance between the sensing structures; and an electroacoustic transducer disposed below the top layer and configured to generate an acoustic wave and direct the acoustic wave toward the sensation through the protective dielectric top layer The surface is sent to sense an ultrasonic vibration potential at the ridge of the finger, the finger ridge being placed in contact with the sensing surface.

Herein, the protective dielectric top layer may be a single layer or may comprise a plurality of stacked layers. Moreover, herein, the layer is dielectric meaning that it is electrically non-conductive, and it can represent a dielectric in a parallel plate capacitor, wherein the two plates are placed on the outer surface of the sensing device. The upper finger and each of the conductive sensing structures are represented. Accordingly, a two-dimensional array of conductive sensing structures is disposed below the top layer, which does not preclude the possibility of having additional layers disposed between the sensing structure and the outer surface of the sensing device. Moreover, the electroacoustic transducer is disposed below the top layer, which is herein interpreted to mean that the electroacoustic transducer is disposed below the top layer when viewed from the outer detection surface of the sensing device (or below). Thus, an additional layer can be disposed between the electroacoustic transducer and the top layer, as will be explained below.

An electroacoustic transducer converts an electrical signal into an acoustic signal to provide an acoustic wave having a frequency that is typically in the ultrasonic range, ie, above the audible frequency. When the finger is placed on the surface of the fingerprint sensing device, the ridge of the finger is in contact with the surface, however the valley of the finger is not in contact with the surface. A portion of the sound wave that reaches the interface between the top layer and the ridge of the finger penetrates into the finger, and a portion of the sound wave that reaches the interface between the top layer and the air is reflected, because The acoustic impedance between the top layer and the air has a large difference. Then, the portion of the sound wave that penetrates the finger generates an induced ultrasonic vibration potential, which can be borrowed Detected by a capacitive fingerprint sensing device. The mechanism behind the generation of ultrasonic vibration potential by the finger will be discussed in further detail in [Embodiment].

Accordingly, the present invention is based on the realization that the improvement in capacitive fingerprint sensing can be achieved by providing a fingerprint sensing device capable of sensing an ultrasonic vibration potential in a finger by means of an electroacoustic transducer. Thereby generating a potential that can be detected by the sensing structure. Thus, an improvement in the capacitive coupling between the ridge of the finger and the sensing structure is achieved, and the effect of the valley from the capacitance measurement (i.e., the influence of the background) is reduced. This is in contrast to existing techniques in which potentials are controllably introduced into the fingers by galvanic coupling or capacitive coupling to the fingers, thus the entire finger, ie the ridges and valleys. , are placed in the same potential level. In contrast, the above-described detecting device induces a potential only in the ridge of the finger, thereby providing a greater contrast between the ridge and the valley, thereby improving the contrast of the capacitance measurement.

The above concepts of the present invention are also applicable as an enhancement to existing capacitive fingerprint sensing techniques in which non-acoustic devices have been used to generate potential at the finger in existing capacitive fingerprint sensing techniques. Moreover, the present invention opens up new opportunities associated with the structure of the sensing device, as these non-acoustic devices for introducing potential at the fingers may be reduced.

According to an embodiment of the invention, the electroacoustic transducer may be an ultrasonic transmitter configured to generate an ultrasonic wave. Ultrasonic transmitters are a commonly used type of electroacoustic transducer that converts electrical signals into ultrasonic waves, and the characteristics of ultrasonic transmitters are well known to facilitate integration into a fingerprint sensing device.

Moreover, advantageously, the electroacoustic transducer can be a planar electroacoustic transducer because of its advantages in that it can be easily integrated into a planar sensor structure.

In one embodiment of the invention, the electroacoustic transducer can be configured such that the emitted acoustic wave is a plane wave. By setting the sound wave as a plane wave, all portions of the finger that are in contact with the surface of the sensing device, that is, the ridges of all the fingers that are in contact with the surface of the sensing device are simultaneously excited by the penetrating sound waves, and Therefore, an ultrasonic vibration potential is presented. Thus, an image of the entire fingerprint can be obtained immediately by simultaneously measuring the capacitive coupling of all of the sensing structures. In addition, a plane wave is uniform over the entire sensor area, and the magnitude of the induced ultrasonic vibration potential provided by the finger is uniform, which simplifies the capacitance measurement because all the fingers in contact with the sensor can be assumed. Partially affected by the ultrasonic vibration potential is the same.

In one embodiment of the invention, the top layer can be configured to have an acoustic impedance that matches the acoustic impedance of a finger. The portion of the sound wave that is transferred at the interface between the top layer and the finger is determined by the difference in acoustic impedance, where the difference in acoustic impedance is mostly caused by most of the sound wave reflection, and the small difference means that the sound wave can be horizontal. Travel across the interface. Therefore, it is desirable that the material selected for the top layer has an acoustic impedance that is as similar as possible to the acoustic impedance of the finger. The difference in acoustic impedance between air and solid material is typically several orders of magnitude. However, while many solid materials will provide a greater contrast than the acoustic impedance of air, it is desirable to select a material that has an acoustic impedance that is as similar as possible to a finger to avoid or reduce reflection losses at the interface.

According to an embodiment of the invention, the transducer may be a piezoelectric acoustic transducer such as a piezoelectric micromachined ultrasonic transducer, PMUT. The piezoelectric acoustic transducer may comprise a piezoelectric crystal, a piezoelectric ceramic, or a piezoelectric polymer. In addition, the electroacoustic transducer can also be a capacitive micromechanical ultrasonic transducer, CMUT.

According to an embodiment of the invention, the electroacoustic transducer can have the same dimensions as the array of sensing structures, which means that the surface area of the transducer is the same as the overall surface area of the array of sensing structures. . Thus, the transducer can transmit an acoustic wave that induces an ultrasonic vibration potential in a finger above the entire active surface of the fingerprint sensing device.

In accordance with an embodiment of the present invention, the fingerprint sensing device can include a plurality of electroacoustic transducers, each of which has an area corresponding to an area of a sub-array of the array of sensing structures. The sub-array of the array of sensing structures can be, for example, a conventional n x m array in which n and m can be selected based on the desired number of electroacoustic transducers. Additionally, the plurality of electroacoustic transducers can be individually controllable such that which transducer can be selected to function at any given time. This can be advantageous, for example, if the finger is only placed in a portion of the area of the fingerprint sensing device, or if it is desired to enhance contrast in a particular region. Therefore, the plurality of electroacoustic transducers provide greater flexibility in acquiring fingerprint images. The total area of the plurality of electroacoustic transducers may correspond to a total area of the array of sensing devices, or the plurality of electroacoustic transducers may be configured to cover only selected portions of the array of sensing structures. Furthermore, in a fingerprint sensing device comprising a plurality of electroacoustic transducers, which transducer can be selected for use in a particular measurement, as compared to sensing that includes only one transducer covering the entire sensing region. Device, which results in reduced energy consumption.

According to an embodiment of the invention, an array of sensing structures may be disposed between the transducer and the protective dielectric top layer. Thus, the distance between the sensing array and the finger does not increase as compared to conventional capacitive fingerprint sensing devices. Furthermore, by forming a stacked layer of the electroacoustic transducer at the bottom under the sensing structure, a capacitive fingerprint sensing device can be fabricated in accordance with known methods without modifying the manufacturing process to accommodate the electroacoustic transducer. The electroacoustic transducer can thus be easily integrated into existing manufacturing solutions. In addition, since the sound wave does not interfere or shadow Capacitive sensing, the acoustic wave can pass through the sensing structure and associated circuitry without adverse effects, or only negligible adverse effects.

According to an embodiment of the invention, the sensing device may further comprise a retardation layer disposed between the electroacoustic transducer and the array of sensing structures. The retardation layer increases the time at which the generated sound waves reach the finger. Advantageously, the retardation layer is placed between the electroacoustic transducer and the array of sensing structures, ie below the array of sensing structures. The delay layer can be like plastic material or PMMA. The effects and advantages associated with the delay layer will be discussed in further detail below with respect to methods for controlling fingerprint sensing devices.

According to an embodiment of the invention, the sensing device may further include a shielding layer disposed between the electroacoustic transducer and the array of sensing structures to sense the electroacoustic transducer The array of measured structures is electrically shielded. Even if the sound wave does not cause electromagnetic distortion or only limited electromagnetic distortion, the electroacoustic transducer can generate an electromagnetic field during the generation of the acoustic wave, thereby affecting the sensing structure during capacitive sensing. Therefore, the shielding layer can reduce or eliminate the influence of the electromagnetic field on the sensing structure.

According to an embodiment of the invention, the shielding layer may comprise a conductive structure that is connected to a ground potential to electromagnetically shield the sensing structure from the electroacoustic transducer. The conductive structure may be a continuous layer, a single structure, an array of grid structures, and the like.

According to an embodiment of the invention, an electroacoustic transducer may be disposed between the array of sensing structures and the protective top layer. Because the electroacoustic transducer can be made of a non-conductive material, such as a piezoelectric material, the electroacoustic transducer can be placed in the sensing as long as the electroacoustic transducer has no conductive structure to shield the sensing structure from the finger. Between the structure and the array of protective top layers.

According to a second aspect of the present invention, there is provided a method for controlling a capacitive finger A method of sensing a sensing device, the capacitive fingerprint sensing device comprising: a protective dielectric top layer having an outer surface to form a sensing surface touched by a finger; a two-dimensional array of conductive sensing structures The system is disposed under the top layer; a read circuit system is coupled to each of the conductive sensing structures to receive a sensing signal, the sensing signal indicating the finger and the sensing structure And an electroacoustic transducer disposed below the top layer, the method comprising: enabling the electro-acoustic transducer to generate an acoustic wave and passing the protective dielectric top layer The sound wave is sent toward the sensing surface to induce an ultrasonic vibration potential at the ridge of the finger, the ridge of the finger is placed in contact with the sensing surface; and a primary fingerprint image is acquired by the reading A circuit system is taken to read the capacitive coupling between the finger and each of the sensing structures.

The above method outlines obtaining a fingerprint using a capacitive fingerprint sensing device, the capacitive fingerprint sensing device including an electro-acoustic transducer to generate an acoustic wave to induce an ultrasonic vibration potential at a ridge of the finger, The ridges of the fingers are placed in contact with the sensing surface. There is no additional potential reference connected to the finger in the sensing device, so the above method can be considered as an enhanced direct capacitance measurement method.

According to an embodiment of the present invention, the method may further include: acquiring an initial fingerprint image before the step of enabling the electro-acoustic transducer; comparing the primary fingerprint image with the initial fingerprint image; and if the initial fingerprint When the difference between the image and the primary fingerprint image is greater than a predetermined threshold, it is determined that the fingerprint image is derived from a real finger. By acquiring an initial fingerprint image prior to activation of the electroacoustic transducer, a reference image is acquired, wherein the finger is unaffected by the sound wave, and wherein there is no ultrasonic vibration potential in the finger. Due to the mechanism of sensing the ultrasonic vibration potential, what is needed is that the substance placed on the fingerprint sensor is Ion or colloidal substance, such as a finger. Therefore, when the electroacoustic transducer is in effect, an inorganic material (such as a rubber or plastic material) placed on the finger does not generate an ultrasonic vibration potential. Therefore, with a fake fingerprint made of rubber or the like, there is no detectable difference between the images acquired before and after the electroacoustic transducer is enabled. Therefore, fake fingerprints can be detected to prevent fingerprint fraud.

Therefore, the reference image is compared with the acquired main image when the electroacoustic transducer acts and the ultrasonic vibration potential is induced at the ridge of the fingerprint, and the difference between the two images can be It is seen as the difference in contrast between the ridge and the valley. Thus, the predetermined threshold may be, for example, a predetermined predetermined average difference between the ridges and valleys of the fingerprint.

If the difference between the initial image and the primary image is greater than a predetermined threshold, for example, if there is a significant difference in the contrast, it can be determined that the fingerprint image is derived from a real finger.

According to an embodiment of the present invention, the method may further include: further comprising: acquiring an initial fingerprint image prior to the step of enabling the electro-acoustic transducer; comparing the primary fingerprint image with the initial fingerprint image; If the difference between the initial fingerprint image and the primary fingerprint image is less than a predetermined threshold, it is determined that the fingerprint image is derived from a fake finger. Similar to the above, if the difference between the initial image and the main image is less than a predetermined threshold, it can be determined that the fingerprint image is derived from a fake finger. Those skilled in the art recognize that the threshold can be defined in a number of different ways, and that the threshold can also be determined empirically for different types of sensing devices and different applications.

Thus, in addition to the improved contrast between the ridges and valleys of the fingerprint, the described sensing apparatus and method also provides effective fraud prevention/site detection.

The additional effects and features of the second aspect of the invention are quite similar to the additional effects and features described above with respect to the first aspect of the invention.

According to a third aspect of the present invention, a method for controlling a capacitive fingerprint sensing device is provided, the capacitive fingerprint sensing device comprising: a protective dielectric top layer having an outer surface to form a a sensing surface touched by a finger; a two-dimensional array of conductive sensing structures disposed below the top layer; a read circuitry coupled to each of the conductive sensing structures to receive a sense Measuring a signal indicating a distance between the finger and the sensing structure; and an electroacoustic transducer disposed below the top layer, the method comprising: enabling the electro-acoustic transducer, Generating an acoustic wave and transmitting the acoustic wave toward the sensing surface through the protective dielectric top layer to induce an ultrasonic vibration potential at the ridge of the finger, the ridge of the finger being placed in contact with the sensing Contacting the surface; deactivating the electroacoustic transducer; and reading the capacitance between the finger and the sensing structure by the read circuitry when the ultrasonic vibration potential of the finger is detectable Sexual coupling to get one finger Images.

By the above method, the ultrasonic vibration potential induced in the finger can be detected, but when the electro-acoustic transducer is deactivated, the fingerprint image is acquired, thereby avoiding the activity of the transducer. The resulting electromagnetic field interferes with the risk of capacitance measurement.

The principle of the method is based on the difference in the propagation speed between the acoustic wave and the electromagnetic field. Thus, in a simplified illustration, the acoustic wave is generated by the transducer and transmitted by the transducer, after which the transducer is deactivated. When the transducer is deactivated, the electromagnetic field from the transducer can be considered to instantaneously become zero. At the same time, the sound wave can be seen as propagating towards the finger. When the sound wave passes through the finger, an ultrasonic vibration potential is induced, and the fingerprint image can be acquired by the reading circuit system. The timing of the capacitance measurement must be controlled so that The time between the deactivation of the transducer and the acquisition of the image is sufficiently short that the effect of the ultrasonic vibration potential in the finger is still detectable.

Advantageously, the described method can be implemented in a fingerprint sensing device that includes a retardation layer as described above. The delay layer establishes a time interval during which the acoustic wave penetrates the finger while the transducer is deactivated, thereby eliminating the adverse effects of the electromagnetic field generated by the transducer of the capacitive sensing structure. The retardation layer can be configured in a number of different ways as long as the generated sound waves can pass through the retardation layer on the route to the finger.

The additional effects and features of the third aspect of the invention are quite similar to the additional effects and features described above with respect to the second aspect of the invention.

Further features and advantages of the present invention will become apparent upon a study of the appended claims. It is apparent to those skilled in the art that the various features of the invention can be combined to produce other embodiments than those described below without departing from the scope of the invention.

100‧‧‧Mobile Phone

102‧‧‧Fingerprint sensing device

104‧‧‧ fingers

105‧‧‧Sensing surface

106‧‧‧Top layer

108‧‧‧Sensor structure

110‧‧‧Substrate

112‧‧‧Electronic sound transducer

114‧‧‧ Valley Department

116‧‧‧ ridge

118a‧‧‧electrode/electrode layer

118b‧‧‧electrode/electrode layer

402‧‧‧Sensor components

404‧‧‧Charging amplifier

406‧‧‧Operational Amplifier

408‧‧‧ first input

410‧‧‧second input

412‧‧‧ output

414‧‧‧ feedback capacitor

416‧‧‧ switch

418‧‧‧Reading circuit system

500‧‧‧Fingerprint sensing device

502‧‧‧Delay layer

600‧‧‧Fingerprint sensing device

602‧‧‧Encapsulation layer

604‧‧‧Adhesive layer

606‧‧‧protection board

608‧‧‧ outermost layer

700‧‧‧Sensing device

702a‧‧‧ electroacoustic transducer

702b‧‧‧ electroacoustic transducer

These and other aspects of the invention will now be described in more detail, with reference to the embodiments illustrated in the drawings of the invention, wherein: FIG. 1 schematically shows a mobile telephone comprising a fingerprint sensing device Figure 2 schematically shows a fingerprint sensing device in accordance with one embodiment of the present invention; Figures 3A-3D schematically illustrate the displacement of a charge carrier due to acoustic waves; Figure 4 is an implementation in accordance with the present invention; A schematic diagram of a portion of a readout circuitry in a fingerprint sensing device; Figure 5 is a schematic representation of a fingerprint sensing device in accordance with one embodiment of the present invention; Figure 6 is a schematic illustration of a fingerprint sensing device in accordance with one embodiment of the present invention; Figures 7A-7B are implemented in accordance with the present invention A schematic diagram of a sensing device of the example; and Figures 8A-8C are flow diagrams that generally depict the general steps of a method in accordance with an embodiment of the present invention.

In the detailed description, various embodiments of systems and methods in accordance with the present invention are described primarily with reference to a capacitive fingerprint sensing device that is suitably configured in an electronic device, such as a mobile telephone. However, it should be noted that various embodiments of the fingerprint sensing device may be suitable for use in other applications.

FIG. 1 schematically shows an application for a fingerprint sensing device 102 in accordance with an exemplary embodiment of the present invention in the form of a mobile phone 100 having an integrated fingerprint sensing device 102. The fingerprint sensing device illustrated here is disposed under the glass cover of the mobile phone 100. The fingerprint sensing device 102 can also be configured in a button, on the side of the phone, or on the back.

The fingerprint sensing device 102 can, for example, be used to unlock the mobile phone 100 and/or to authorize the use of the mobile phone for transactions... and the like. The fingerprint sensing device 102 in accordance with various embodiments of the present invention may also be used in other devices, such as tablets, notebooks, smart cards, or other types of consumer electronics.

2 is a schematic cross section of a portion of fingerprint sensing device 102 in accordance with one embodiment of the present invention with a finger 104 placed on the outer surface of sensing device 102. The finger The pattern sensing device 102 includes a protective dielectric top layer 106 having an outer surface for forming a sensing surface 105 for a finger to touch. A two-dimensional array of conductive sensing structures 108 are disposed under the top layer 106, and a read circuitry is coupled to each of the conductive sensing structures 108 to receive a sensed signal indicative of the The distance between the finger and the sensing structure. The array of sensing structures 108 is illustrated herein as being disposed on a substrate 110, wherein the substrate can include at least a portion of the read circuitry. The substrate 110 can be, for example, a germanium substrate, and the fingerprint sensing device 102 can be fabricated using conventional fabrication techniques compatible with germanium.

Additionally, the sensing device 102 includes an electro-acoustic transducer 112 disposed below the top layer 106. In FIG. 2, the electroacoustic transducer 112 is disposed below the substrate 110. The electroacoustic transducer 112 is configured to generate an acoustic wave and transmit the acoustic wave toward the sensing surface 105 through the protective dielectric top layer 106 to induce an ultrasonic vibration potential at the ridge 116 of the finger 104. The ridge 116 of the finger 104 is placed in contact with the sensing surface 105. In the illustrated embodiment, the acoustic wave passes through the substrate 110 before reaching the protective dielectric top layer 106. It should be noted that even though the substrate 110 and the top layer 106 are shown as individual single layers, both of the above may include a plurality of layers, ie, including stacked layers, as will be related to various embodiments of the present invention. Further details are discussed.

The electroacoustic transducer 112 can be a plane wave generator. The electroacoustic transducer 112 shown in FIG. 2 includes a sheet of piezoelectric material sandwiched between a first metal electrode layer 118a and a second metal electrode layer 118b. The piezoelectric sheet may be made of a piezoelectric ceramic, a piezoelectric crystal, or a piezoelectric polymer. The metal electrode layers 118a-118b can be deposited or mounted on either side of the piezoelectric sheet in a number of different ways well known to those skilled in the art. By applying an electrical signal to the electrodes 118a-118b of the plane wave generator as described above, a flat pattern will be generated The scattered sound waves, that is, the sound wave energy is evenly distributed in the wavefront.

The electroacoustic transducer 112 can be a piezoelectric acoustic transducer based on a piezoelectric micromachined ultrasonic transducer, a PMUT, or a capacitive micromachined ultrasonic transducer, CMUT. The electroacoustic transducer 112 can also be referred to as an ultrasonic transmitter in some cases. As an example, the frequency of the sound wave is in the range of 10 MHz to 100 MHz.

The fingerprint sensing device 102 utilizes an induced ultrasonic vibration potential in a finger. The mechanism for generating an ultrasonic vibration potential in the human body is described below.

It is known that the propagation of longitudinal ultrasonic waves through the electrolyte causes the generation of alternating potential differences within the solution. These alternating potentials were initially predicted as simple ionic solutions. Any difference in the effective mass or coefficient of friction between the anion and the cation in the presence of longitudinal sound waves will result in different magnitudes of displacement. As a result, this difference in displacement causes an alternating potential between multiple points within the solution. This phenomenon is sometimes referred to as "ion vibration potential", which is an ultrasonic vibration potential.

The mechanism of the generation of the ion vibration potential is schematically shown in Fig. 3A, which shows a displacement at a specific moment on the Y-axis and a distance in the propagation direction on the X-axis. The condition shown here is that the area A will be positively charged with respect to the area B. If the inert metal probe is placed at positions A and B, an alternating potential difference will be observed because the curve representing the displacement can be considered to advance in the forward direction in the traveling sound field at the speed of the acoustic wave. The frequency of the alternating potential corresponds to the frequency of the sound field.

It has been shown that no matter how complex these materials are, for example, proteins or polyions in a solution of a multi-electrolyte, the ion vibrational potential is generated at every instant, wherein the ultrasonic waves propagate through the solution containing the ionic species.

Ultrasonic vibrational potential has also been shown to occur in colloidal suspensions. A colloid is a suspension of charged particles in a liquid in which each particle is surrounded by an opposite charge distribution, as shown in Figure 3B. The opposite charge typically has a spherical distribution around the particles, so it gives a solution to the overall charge neutrality and stabilizes the suspension without causing particle agglomeration. When the sound propagates through the suspension, where the density of the particle is higher or lower than the density of the surrounding liquid, the magnitude and phase of the particle motion is due to the difference in inertia between the volume of the particle and the displacement of the liquid. It will differ from the amplitude and phase of the liquid so that the back and forth flow of the liquid relative to the particles will have a phase of change in the acoustic cycle. Because the liquid carries an opposite charge, the oscillating motion of the liquid relative to the particles causes distortion of the generally spherical opposite charge distribution, thereby creating an oscillating dipole at the location of each particle, which results in a large voltage. This ultrasonic vibration potential is called a "colloidal vibration potential". The generation of the colloidal vibration potential is schematically shown in Figures 3C-3D.

Figure 3C shows colloidal particles and opposite charges in the presence of acoustic waves, where the two dipoles oscillate in opposite phases to each other. At the point in time shown in Figure 3C, region A is negatively charged relative to region B.

Figure 3D shows the lower half of the acoustic wave, where the dipole has moved to the opposite phase such that region A is positively charged relative to region B. Therefore, it can be understood that a periodic ultrasonic vibration potential is formed, the ultrasonic vibration potential having the same frequency as the acoustic wave.

The human body is a relatively good conductor of electricity. This is due to the electrolyte properties of body fluids in the human body. For example, sodium chloride in water is broken down into positively charged sodium ions and negatively charged chloride ions.

In addition, the strongest ultrasonic vibration potential signal detected to date in biological samples is derived from blood. Due to the fact that blood is both colloid (due to the presence of red blood cells) and is ionic (because of the dissolved electrolyte), it causes a greater vibrational potential. This can be exploited to develop a more secure fingerprint sensor where the presence of organic tissue and blood can be used to sense the ultrasonic vibration potential in the finger.

As shown in FIG. 2, a longitudinal acoustic wave is generated by the ultrasonic transducer 112. The resulting travel toward the finger. When the sound wave reaches the interface between the top layer 106 and the finger 104, two possible situations occur. If the interface is caused by the valleys 114 of the fingerprint, most of the energy reaching the sound waves will be reflected due to the large mismatch between the acoustic impedance of the air and the top layer 106. On the other hand, most of the arriving acoustic energy will penetrate the fingers 104 at the portion of the interface where the ridges 116 of the fingers are in direct contact with the top layer 106.

The ultrasonic waves penetrate the finger tissue at the ridge 116, which will create a periodic potential, i.e., an ultrasonic vibration potential, within the tissue. Thus, this causes a periodic electric field to appear between the ridge 116 of the fingerprint and the sensing structure 108 disposed below the ridge 116 of the fingerprint and maintained at a fixed potential level. This time varying electric field is then sensed by the sensing structure 108 and registered by the read circuitry, as shown schematically in FIG.

4 is a schematic cross-sectional view and circuitry diagram of a portion of fingerprint sensing device 102 in accordance with an embodiment of the present invention with a fingerprint ridge 116 positioned above the sensing structure 108. The fingerprint sensing device includes a plurality of sensing elements 402, each of which includes a protective dielectric top layer 106, a conductive sensing structure 108, and a metal plate beneath the protective dielectric top layer 106. In the form of 108, a charging amplifier 404. As shown in Figure 4, the hand The ridge 116 of the finger 104 is directly above the sensing structure 108, indicating that the minimum distance between the finger 104 and the sensing structure 108 is defined by the dielectric top layer 106.

The charging amplifier 404 includes at least one amplifier stage, which is schematically shown as an operational amplifier 406 (op amp) having a first input (negative input) 408 coupled to the sensing structure 108, A second input (positive input) 410 is coupled to ground (or another reference potential) and an output 412. Additionally, charging amplifier 404 includes a feedback capacitor 414 coupled between the first input 408 and the output 412 and a reset circuitry, shown as a switch 416 for allowing control of the feedback capacitor 414. Discharge. The charge amplifier 404 can be reset by operating the reset circuitry 416 to discharge the feedback capacitor 414.

It is common for an operational amplifier 406 to be in a negative feedback configuration where the potential at the first input 408 follows the potential applied to the second input 410. Depending on the particular amplifier configuration, the potential at the first input 408 can be substantially the same as the potential at the second input 410, or the potential at the first input 408 and the potential at the second input 410. There can be a substantially fixed offset between the potentials. In the configuration of Figure 4, the first input 408 of the charging amplifier is virtually grounded.

When a finger is placed on the sensing surface, a potential difference is generated between the sensing structure 108 and the ridge 116 of the fingerprint. The induced change in potential difference between the ridge 116 of the fingerprint and the reference sense structure 108 thus causes a sensed voltage signal Vs on the output 412 of the charge amplifier 404, wherein the amplitude of the voltage is the ridge 116 of the fingerprint. And a function of the capacitive coupling between the sensing structure, and thereby indicating the presence of an induced vibration potential. The sense voltage signal Vs is thus provided to the read circuitry 418, wherein sensing from the array of image sensing elements The voltage signals together form a fingerprint image.

As with reference to FIG. 2 above, the electroacoustic transducer 112 generates an acoustic wave that is transmitted through the protective dielectric top layer 106 toward the sensing surface to induce ultrasonic vibration of the ridge 116 of the finger. The potential, thus creating a sound field in the finger. According to the mechanism described above, the sound field produces an ultrasonic vibration potential at the ridge of the finger, the ridge of the finger being placed in contact with the sensing surface. Thereby, the induced ultrasonic vibration potential can be detected by the charging amplifier 404, and a fingerprint image can also be acquired in one case, in which case the ridge and the valley of the finger are capacitively coupled to the sense Measuring the difference in structure is not enough to produce an accurate fingerprint image. This may be the case with a thick top layer, such as a glass cover or display glass. Therefore, the electroacoustic transducer does not participate in the reading of the sensing signal.

In FIG. 4, the charge amplifier 404 and read circuitry are shown primarily in the substrate 110. However, selected portions of the charging amplifier and reading circuitry may also be located below the electroacoustic transducer, wherein, for example, an electrical connection, such as a via connection, may be used to connect the charging amplifier to the sensing structure.

FIG. 5 is a schematic diagram of an exemplary embodiment of a fingerprint sensing device 500 in which a retardation layer 502 is disposed between an array of electroacoustic transducers 112 and a sensing structure 108. The purpose of the retardation layer 502 is to increase the time that the generated sound waves reach the finger 104, and thus increase the time from when the sound wave is generated to when the acoustic vibration potential is generated at the finger. Most preferably, the retardation layer 502 has low acoustic attenuation and thus the acoustic energy of the lost acoustic energy can be reduced as the acoustic waves travel through the retardation layer 502. It is also preferred that the acoustic impedance of the retardation layer 502 is similar to the acoustic impedance of an adjacent layer (here the substrate 110) to reduce reflection at the interface between the retardation layer 502 and the substrate 110. The retardation layer 502 can comprise a plastic material, polymethyl methacrylate (PMMA), or A dielectric material that has known acoustic properties. For example, the retardation layer can be selected such that at least 10%, preferably 50%, and more preferably 90% of the incident energy passes through the retardation layer. The advantages of this retardation layer will be further discussed below in relation to a method for controlling a fingerprint sensing device.

FIG. 6 is a schematic diagram of an exemplary embodiment of a fingerprint sensing device 600. In the fingerprint sensing device of FIG. 6, the stacked layer disposed over the array of sensing structures 108 includes an encapsulation layer 602 or a capping layer, an adhesive layer 604, and an outermost layer 608. To protect the sensing structure, the adhesive layer 604 is used to attach a protective sheet 606 (eg, a glass cover) to the sensing device, the outermost layer 608 can be a colored or patterned coating that provides The desired aesthetic appearance of the fingerprint sensor 600. Thus, all of the above layers together form the dielectric top layer 106. Those skilled in the art will recognize that the stacked layers described can have many different ways to form embodiments not explicitly described herein. Moreover, the layers described herein are generally continuous and are substantially homogeneous uniform layers.

The outermost layer 608 can also be a matching layer configured to match the acoustic impedance of the underlying layer (here the protective plate 606) to the acoustic impedance of the finger 104. Advantageously, the acoustic impedance of the matching layer can be the geometric mean of the acoustic impedance of the finger and the acoustic impedance of the underlying layer. By matching the acoustic impedance, portions of the acoustic waves reflected at the interface between the outermost layer and the finger can be minimized, thereby maximizing the induced ultrasonic vibration potential.

FIG. 7A is a schematic illustration of a sensing device 102 that includes a single electroacoustic transducer 112 that is the same size as the array of sensing structures 108. In contrast, FIG. 7B is a schematic diagram of a sensing device 700 that includes a plurality of electroacoustic transducers 702a-702b, each of which has an area corresponding to a sub-area of the array of sensing structures 108. Thus, each electroacoustic transducer can be individually controlled such that only selected transducers are enabled. For the sake of clarity, the sensing devices in Figures 7A-7B are illustrated as having no top layer.

FIG. 8A is a flow diagram that simply depicts a general procedure in a method for controlling a fingerprint sensing device in accordance with an embodiment of the present invention. In a fingerprint sensing device according to any of the above embodiments, the electroacoustic transducer is enabled 802 by providing a supply voltage that is converted such that an acoustic wave system is generated 804. The sound wave is then sent 806 to the finger such that an ultrasonic vibration potential is induced in the finger. Once the ultrasonic vibration potential is induced, a fingerprint image is acquired 808 by reading a capacitive coupling between the finger and the sensing structure of the sensing array.

Since the ultrasonic vibration potential is a periodic potential and has a frequency corresponding to the acoustic wave frequency, it is preferred that the potential is at a region where the finger is closest to the sensing surface and at a maximum amplitude or near At the maximum extent, the fingerprint image is acquired.

Figure 8B is a flow chart that simply depicts a general procedure in a method for controlling a fingerprint sensing device in accordance with an embodiment of the present invention. First, the electroacoustic transducer is deactivated and an initial fingerprint image is acquired 810. Following 812, the electro-acoustic transducer is enabled, a sound system is generated and transmitted to the finger, and a second, primary fingerprint image is acquired 814. The initial image is compared 816 to the primary image, and if the difference is greater than the predetermined threshold 818, then the fingerprint acquired by the 820 system is determined to originate from a real finger. If the difference between the initial image and the primary image is less than a predetermined threshold, then the fingerprint acquired 822 is derived from a fake finger. It should also be noted that the above method can be combined with other components. In order to effectively carry out on-site detection for further prevention of fraud.

Figure 8C is a flow diagram that simply depicts a general procedure in a method for controlling a fingerprint sensing device in accordance with an embodiment of the present invention. In a first step 812, the electroacoustic transducer is enabled and an acoustic wave system is generated and transmitted to the finger. Then, the electro-acoustic transducer is deactivated 824, and when the ultrasonic vibration potential on the finger can be detected, a fingerprint of 826 is obtained by reading the capacitive coupling between the finger and the sensing structure. image. Advantageously, the method can be implemented in a sensing device 500 including a retardation layer 502, as shown in FIG. By adjusting the thickness and acoustic characteristics of the retardation layer, the retardation layer can be configured to delay the acoustic wave such that the electroacoustic transducer is deactivated while the ultrasonic vibration is simultaneously in the finger while acquiring a fingerprint image The potential can still be detected. Thereby, the distortion caused by the electromagnetic field generated by the electroacoustic transducer can be avoided. In the actual case, it is preferred that the fingerprint image can be acquired as soon as the electro-acoustic transducer is deactivated because the ultrasonic vibration potential is attenuated.

The method described in relation to Figure 8C can also be combined with the method illustrated in Figure 8B. Thus, in a method for determining whether a fingerprint is authentic or falsified, the primary fingerprint image can be acquired using a method as briefly described in FIG. 8C, wherein after the electroacoustic transducer has been deactivated, a fingerprint system is Acquire, but at the same time there is still a detectable ultrasonic vibration potential in the finger.

In addition, it should be noted that although the present invention is directed to the described capacitive sensing device, the techniques of the electroacoustic transducer utilized herein can be used to directly or indirectly detect the induced potential in a finger. Any type of sensing device is integrated. Such sensing devices include electric field sensing devices, and the like.

While the invention has been described with reference to the specific embodiments of the embodiments of the invention In addition, it should It is pointed out that the components and methods of the fingerprint sensing device can be omitted, interchanged, or configured in a variety of ways, but the fingerprint sensing device is still capable of performing the functions of the present invention.

In addition, variations of the embodiments of the present disclosure can be understood and practiced by those skilled in the <RTIgt; In the scope of the present application, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" The mere fact that certain measures are recorded in mutually different sub-requests does not mean that the combination of these measures cannot be used favorably.

102‧‧‧Fingerprint sensing device

104‧‧‧ fingers

105‧‧‧Sensing surface

106‧‧‧Top layer

108‧‧‧Sensor structure

110‧‧‧Substrate

112‧‧‧Electronic sound transducer

114‧‧‧ Valley Department

116‧‧‧ ridge

118a‧‧‧electrode/electrode layer

118b‧‧‧electrode/electrode layer

Claims (20)

A capacitive fingerprint sensing device for sensing a fingerprint pattern of a finger, the capacitive fingerprint sensing device comprising: a protective dielectric top layer having an outer surface to form one of the touches by the finger a sensing surface; a two-dimensional array of conductive sensing structures disposed under the top layer; a read circuit system coupled to each of the conductive sensing structures to receive a sensing signal, The sensing signal is based on a capacitive coupling between the finger and the respective sensing structures to indicate a distance between the finger and the sensing structure; and an electroacoustic transducer disposed below the top layer, and Configuring to generate an acoustic wave and transmitting the acoustic wave toward the sensing surface through the protective dielectric top layer to induce an ultrasonic vibration potential on a finger ridge, the finger ridge being placed in the sense The surface is measured for contact. The sensing device of claim 1, wherein the electroacoustic transducer is an ultrasonic transmitter configured to generate an ultrasonic wave. The sensing device of claim 1, wherein the electroacoustic transducer is a planar electroacoustic transducer. The sensing device of claim 1, wherein the electroacoustic transducer is configured such that the transmitted acoustic wave is a plane wave. The sensing device of claim 1, wherein the top layer is configured to have an acoustic impedance that matches an acoustic impedance of a finger. The sensing device of claim 1, wherein the electroacoustic transducer is a piezoelectric transducer. The sensing device of claim 6, wherein the electroacoustic transducer is a piezoelectric micromachined ultrasonic transducer, PMUT. The sensing device of claim 1, wherein the electroacoustic transducer is a capacitive micromechanical ultrasonic transducer, CMUT. The sensing device of claim 1, wherein the electroacoustic transducer has the same dimensions as the array of sensing structures. The sensing device of claim 1, comprising a plurality of electroacoustic transducers each having an area corresponding to an area of the sub-array of the array of sensing structures. The sensing device of claim 1, wherein the array of sensing structures is disposed between the transducer and the protective dielectric top layer. The sensing device of claim 11, further comprising a retardation layer disposed between the electroacoustic transducer and the array of sensing structures. The sensing device of claim 12, wherein the retardation layer comprises a plastic material or PMMA. The sensing device of claim 1, further comprising a shielding layer disposed between the electroacoustic transducer and the array of sensing structures to couple the electroacoustic transducer with The array of sensing structures is electrically shielded. The sensing device of claim 14, wherein the shielding layer comprises a conductive structure connected to a ground potential. The sensing device of claim 1, wherein the electroacoustic transducer is disposed between the array of sensing structures and the protective top layer. A method for controlling a capacitive fingerprint sensing device, the capacitive fingerprint sensing device The device includes: a protective dielectric top layer having an outer surface to form a sensing surface touched by a finger; a two-dimensional array of conductive sensing structures disposed below the top layer; Taking a circuit system connected to each of the conductive sensing structures to receive a sensing signal, the sensing signal indicating the finger and the sense based on a capacitive coupling between the finger and each sensing structure Measure the distance between the structures; and an electroacoustic transducer disposed below the top layer, the method comprising: enabling the electroacoustic transducer to generate an acoustic wave and passing the protective dielectric top The layer transmits the sound wave toward the sensing surface to induce an ultrasonic vibration potential at a finger ridge, the finger ridge is placed in contact with the sensing surface; and a primary fingerprint image is obtained by The read circuitry reads a capacitive coupling between the finger and the sensing structure. The method of claim 17, further comprising: obtaining an initial fingerprint image prior to the step of enabling the electro-acoustic transducer; comparing the primary fingerprint image with the initial fingerprint image; and if When the difference between the initial fingerprint image and the primary fingerprint image is greater than a predetermined threshold, it is determined that the fingerprint image is derived from a real finger. The method of claim 17, further comprising: obtaining an initial fingerprint image prior to the step of enabling the electro-acoustic transducer; comparing the primary fingerprint image with the initial fingerprint image; and if The difference between the initial fingerprint image and the primary fingerprint image is less than a predetermined threshold When it is determined that the fingerprint image is derived from a fake finger. A method for controlling a capacitive fingerprint sensing device, the capacitive fingerprint sensing device comprising: a protective dielectric top layer having an outer surface to form a sensing surface touched by a finger; a two-dimensional array of conductive sensing structures disposed under the top layer; a read circuit system coupled to each of the conductive sensing structures to receive a sensing signal, the sensing signal is based on a capacitive coupling between the finger and each sensing structure to indicate a distance between the finger and the sensing structure; and an electroacoustic transducer disposed below the top layer, the method comprising: enabling the An electroacoustic transducer for generating an acoustic wave and transmitting the acoustic wave toward the sensing surface through the protective dielectric top layer to induce an ultrasonic vibration potential in a finger ridge, the finger ridge placement Contacting the sensing surface; deactivating the electroacoustic transducer; and when the ultrasonic vibration potential in the finger is detectable, the reading circuit is used to read the finger The electrical connection between the sensing structures Coupled to acquire a fingerprint image.